Well they do say:

    In the domain of fine art, the area between elements is called negative space, 
    although in other areas of design it’s often referred to as “white space.”

I would check out design for hackers by @kadavy http://www.amazon.com/Design-Hackers-Reverse-Engineering-Bea... He talks a lot about white space

It's negative space.

If your audience is developers, they understand 'whitespace'. 'Negative space' is an ambiguous term that can mean a few things to developers.